Chemical characterization of melt-textured YBCO produced by hybrid powder metallurgy

Monolithic YBCO samples were made by traditional top-seeded melt-texturing processes from cold-milled mixtures of Y123 (YBa2Cu3O7−δ) and elemental Y. The bulk composition does not lie on the Y211 (Y2BaCuO5)–Y123 join so, formation of Y123 from liquid and Y211 is not an essentially isothermal process on cooling. The reaction liquid + Y211 = Y123 is a ternary reaction and occurs over several tens of degrees. The Y123 thus produced has a range in compositions – particularly in Cu:(Y + Ba) – which may reflect crystallization over the thermal interval. The liquid migrates to an invariant point at which CuO also crystallizes with complete loss of liquid. The presence of trains of CuO grains in the YBCO indicates the locations of the last liquids to be preserved in the sample. These trains are dominantly in an annulus 1–3 mm from the edge of the 20-mm diameter sample. Mapping the compositional variation in Y123 may allow mapping the path of crystallization of these monolithic YBCO samples.